Protein synthesis initiation factor 4E (eIF4E) is a mRNA Cap-binding protein involved in an early rate limiting step in the initiation of protein synthesis. eIF4E undergoes phosphorylation at Ser209 in response to growth factors and other extracellular stimuli. In addition, eIF4E undergoes phosphorylation at Thr210 . In cells, eIF4E occurs as a complex with inhibitory binding proteins (4EBP) and as part of the eIF4F complex which also contains eIF4A and eIF4G. In response to insulin and other extracellular stimuli, eIF4E is activated and recruited to the eIF4F complex following its dissociation from the inhibitory 4EBP.

Over-expression of eIF4E leads to cell transformation and tumorigenesis. This dual phosphorylation site mutant (eIE-4ES209AT210A) is used to determine the functional significance of eIF-4E phosphorylation at Ser209 and Thr210.